Abstract
The influences of magnetic particle-particle interactions on orientational distributions and viscosity of a semi-dense dispersion composed of rod-like particles with a magnetic moment magnetized normal to the particle axis were investigated. In addition, the influences of the magnetic field strength, shear rate, and random forces on the orientational distribution and rheological properties were clarified. The mean field approximation was applied to take into account magnetic interactions between rod-like particles. The basic equation of the orientational distribution function was derived from the balance of torques and solved by the numerical analysis method. The results obtained are summarized as follows. For a strong magnetic field, the rotational motion of the rod-like particle is restricted in a plane normal to the shearing plane because the magnetic moment of the particle is restricted in the magnetic field direction. When a very strong magnetic interaction exists between particles, the magnetic moment is strongly restricted in the magnetic field direction, so that the particles tend to incline in the flow direction with the magnetic moment aligned with the magnetic field. For a strong shear flow, the directional characteristic of rod-like particles is enhanced, and this leads to a more significant one-peak-type distribution of the orientational distribution function. Magnetic interactions between particles do not contribute to the viscosity because the mean-field vector has only a component in the direction of the magnetic field.
